We wish to gain further insight into the molecular events leading to radiation-induced cell death, and the molecular basis of the oxygen effect; more specifically, the roles of DNA single-strand and double-strand breaks and base damage, and their enzymic repair, in these two phenomena. BIBLIOGRAPHIC REFERENCES: Enzymatic production of DNA double-strand breaks after ultraviolet irradiation of Escherichia coli K-12. T. Bonura and K. C. Smith, J. Bacteriol. 121, 511-517 (1975). The influence of oxygen on the yield of DNA double-strand breaks in X-irradiated Escherichia coli K-12. T. Bonura, C. D. Town, K. C. Smith and H.S. Kaplan, Radiat. Res. 63, 567-577 (1975).